Jet engine silencer

Abstract

In and for a jet propulsion engine having a thrust nozzle adapted to exhaust a propulsive gas jet, said nozzle including wall means longitudinally bounding a hollow central body substantially coaxial with said nozzle, a silencer device for reducing the noise produced by said gas jet, said silencer device comprising means for supplying the inside of said hollow central body with air, and at least one orifice formed in said wall means and through which air from the inside of said hollow central body can discharge into the gas jet exhausting from said thrust nozzle, wherein the improvement comprises, hingedly connected to the central body, at least one adjustable obturating flap movable between a first position wherein it unmasks said orifice and a second position wherein it masks the same and restores a substantially unbroken surface to the longitudinal wall of the central body.

Description

The present invention relates to a silencer device for reducing the noise produced by a propulsive gas jet exhausting from the thrust nozzle of a jet propulsion engine, said nozzle including wall means longitudinally bounding a hollow central body substantially coaxial with said nozzle, said silencer device being of the kind comprising means for supplying the inside of said hollow central body with air, and at least one orifice formed in said wall means and through which air from the inside of said hollow central body can discharge into the said gas jet.

The invention has for its object, firstly, to improve the noise abatement effect resulting from placing the gas jet in contact with air issuing from the hollow central body and, secondly, to allow of cancelling this noise abatement effect when it is no longer required.

In accordance with the invention, there is provided, hingedly connected to the central body, at least one adjustable obturating flap movable between a first or operative position wherein it unmasks the aforesaid orifice, and a second or inoperative position wherein it masks the same and restores a substantially unbroken surface to the longitudinal wall of the central body.

In accordance with an embodiment of the invention, the flap comprises a hollow body having an open upstream end which always lies inside said central body, and a likewise open downstream end which when said orifice is masked lies inside the central body and when said orifice is unmasked projects into the gas jet.

In accordance with another embodiment of the invention, the silencer further includes a generally dihedronshaped deflector member supported by the central body and capable of occupying either an operative or deployed position wherein it projects into the gas jet and its edge extends substantially transversely to the nozzle axis, the interior of said dihedron then facing downstream, or an inoperative position wherein it is retracted into said central body.

The description which follows with reference to the accompanying non-limitative exemplary drawing will give a clear understanding of how the invention can be carried into practice.

In the drawing:

FIG. 1 is a diagrammatic illustration in axial section of an embodiment of a jet engine silencer, in which a silencing effect is obtained by injecting fresh air from an air pocket situated inside the central body through orifices formed in the wall thereof, into the gas jet exhausting from the nozzle, said central body being equipped with adjustable obturating flaps;

FIG. 2 is a schematic view in perspective of the central body forming part of the silencer shown in FIG. 1;

FIG. 3 is a detail view illustrating an alternative embodiment in which the silencer is equipped with an air ejector for improving the supply of the inside of the central body with air drawn in from outside the jet engine;

FIG. 4 diagrammatically illustrates a further alternative embodiment in which the inside of the central body is supplied with air tapped from the by-pass flow of a dualflow jet engine;

FIG. 5 diagrammatically illustrates yet another alternative embodiment in which the inside of the central body is supplied with air tapped from between two engine compressor stages;

FIG. 6 diagrammatically illustrates still another alternative embodiment in which two obturating flaps cooperate with the same orifice in the central body wall, said flaps being shown in their operative or silencing position;

FIG. 7 is a view corresponding to FIG. 6 but in which said flaps are shown in their inoperative position;

FIG. 8 diagrammatically illustrates a further alternative embodiment in which the obturating flaps assume the form of hollow bodies, said flaps being shown in their operative or silencing position;

FIG. 9 diagrammatically illustrates yet another alternative embodiment in which a dihedron-shaped deflecting member projects, in its operative position, through an orifice in the central body;

FIG. 10 is a view corresponding to FIG. 9, further depicting flaps for masking said orifice when the dihedron-shaped deflecting member is retracted into its inoperative position;

FIG. 11 diagrammatically illustrates another arrangement of the invention in which an auxiliary fairing surrounds, in its operative or silencing position, the central body in the region of the orifice formed therein; and

FIG. 12 is a view corresponding to FIG. 11 but in which said auxiliary fairing is in its inoperative position.

In all the figures in the drawing, like parts are designated by like reference numerals.

Reference is first had to FIGS. 1 and 2, in which reference numeral 1 designates a jet propulsion engine terminating downstream in a thrust nozzle 2, of axis X'-X, from which exhausts in operation a gas jet F.

The gas jet F flows through a passage 3 bounded by the nozzle 2, which nozzle terminates downstream in a discharge edge 2a. A central body 5 coaxial with said nozzle extends rearwardly beyond the discharge edge 2a thereof. Central body 5 is supported by a cowling 4 through the agency of hollow streamlined struts 6 extending across the flow passage 3.

The central body 5 has a wall 7 longitudinally bounding a pocket 8 in the inside of said central body, which pocket is connected through the hollow struts 6 with the surrounding atmosphere, whereby said pocket 8 can be supplied with air drawn in from outside the jet engine, as shown by the arrow f.

Means are provided for placing the gas jet F in contact with air issuing from the inside of central body 5. These means include at least one but preferably several orifices 9 formed in the longitudinal wall 7 of the central body and through which air from the air pocket 8 can be injected into the gas jet F as shown by the arrow .phi..

Adjustable obturating flaps cooperate with the orifices 9 and include, in respect of each orifice 9, a flap 10 hingedly connected to the central body 5 and angularly adjustable in relation thereto. In the example illustrated, each flap 10 is hingedly connected to central body 5 about a hinge-pin 11 extending transversely in relation to the nozzle axis. Each flap 10 includes a wall element 10a adapted to mask the associated orifice 9 whereby to restore a substantially unbroken surface to central body wall 7, and two side walls 10b, 10c, substantially parallel to nozzle axis X'-X and interconnected, inter alia, by a stud 12.

Actuating means allow of pivoting the flaps 10 about the hinge-pins 11 between an operative position (shown in FIGS. 1 and 2) wherein the orifices 9 are unmasked, and an inoperative position wherein the same are masked. In the embodiment shown in FIGS. 1 and 2, the actuating means include, in respect of each flap 10, a link 13 having one of its ends hingedly connected to stud 12 and its other end fast with the rod 14a of a fluid-operated actuator 14 common to all the flaps 10 and housed inside central body 5.

In operation, when the flaps 10 are in their operative positions shown in FIGS. 1 and 2, they unmask the orifices 9 and at the same time project into the gas jet F whereby to cause the internal cross-sectional profile thereof to assume a corrugated outline having a great perimeter.

At the location of each corrugation in said outline, an air jet .phi. is thus injected into said jet through the associated orifice 9. The gas/air mixing surface is thereby greatly increased, which helps to reduce the noise produced by the gas jet.

When the silencing effect is no longer required, the actuator 4 is operated in the direction causing the flaps 10 to assume their inoperative position (not shown) in which they mask the orifices 9 and restore a substantially unbroken surface to central body wall 7. The internal cross-sectional outline of the gas jet F then resumes its normal non-corrugated shape and the injection of air through the orifices 9 is stopped.

FIG. 3 relates to an alternative embodiment with respect to FIGS. 1 and 2, in which, in order to increase the rate at which air is sucked in from outside the nozzle, there is disposed within the hollow strut 6 or within central body 5 a jet pump or ejector 30 supplied with pressurized inducing fluid through a conduit 31. Such ejector is preferably of the divergent fluid-wall type described in the applicant's U.S. Pat. No. 3,216,653. In cases where nozzle 2 forms part of a turbojet engine, the said pressurized fluid may advantageously be pressurized air tapped from a compressor of such turbojet.

FIG. 4 depicts an alternative embodiment with respect to those illustrated in FIGS. 1 to 3, applicable in cases where jet engine 1 is of the dual-flow or by-pass type and produces a high-pressure and heated gas flow F.sub.1 and a low-pressure unheated air flow F.sub.2 which is lightly compressed by an upstream fan 40. In such cases, the air pocket 8 can be supplied with air through one or more conduits 41 each of which is formed with an inlet orifice 41a, disposed in such manner as to tap fresh air from the low-pressure unheated air flow F.sub.2, and an outlet orifice 41b opening into said air-pocket.

FIG. 5 illustrates another alternative embodiment in which the air-pocket 8 is supplied with air through a passageway 50 originating between two stages of a multi-stage compressor and opening into said air-pocket. In the illustrated example, the compressor is of the dual-spool type with a low-pressure spool 51 and a high-pressure spool 52, and the passageway 50 originates between the two compressor spools.

FIGS. 6 and 7 illustrate yet another alternative embodiment with respect to the one depicted in FIGS. 1 and 2, wherein the obturating flaps include, in respect of each orifice 9, a pair of flaps 60 and 61 disposed one after the other longitudinally along the nozzle and hinged to the central body, by their upstream and downstream edges respectively, about hinge-pins 62 and 63 extending transversely of the nozzle.

Each flap 60 (or 61) includes a longitudinal wall element 60a (or 61a) adapted to mask part of the associated orifice 9 and to thereby restore a substantially unbroken surface to the wall 7 of the central body.

Each flap 60 additionally includes two side walls 60b and 60c substantially parallel to the nozzle axis X'-X, and each flap 61 is movable between two fixed side walls 64b and 64c supported by the central body and extending substantially parallel to said axis.

Each flap 60 of a pair of flaps 60, 61 is fast with an actuating arm 65 connected through a link 66 to a similar actuating arm 67 fast with the companion flap 61, whereby upon one of said flaps (for example flap 60) pivoting towards the nozzle axis the other flap simultaneously pivots away therefrom. Each of actuating arms 67 is hingedly connected to the end of the rod 68a of an actuator 68 common to all the pairs of flaps 60-61 and housed inside central body 5.

In operation, when flaps 60 and 61 are in their operative position shown in FIG. 6, they unmask the orifices 9, whereby air jets .phi. are injected into the gas jet F to produce a silencing effect. When the silencing effect is no longer needed, actuator 68 is activated to move the flaps 60 and 61 into their inoperative position (shown for example in FIG. 7), thereby masking the orifices 9 and restoring a substantially unbroken surface to the wall 7 of the central body. The injection of fresh air through orifices 9 is then stopped.

FIG. 8 shows yet another alternative embodiment in which each orifice 9 formed in the wall 7 of central body 5 cooperates with a flap 80 hingedly connected to the central body about a hinge-pin 81 extending transversely of the nozzle axis.

Each flap 80 is in the shape of a hollow body having three closed faces 80a, 80b and 80c, an open upstream end 80d and a likewise open downstream end 80e. The upstream end 80d always lies inside the air-pocket 8 irrespective of the position of flap 80.

In operation, when flap 80 is in its operative position (shown in FIG. 8) the orifice 9 is unmasked and the downstream end 80e of the flap projects into the gas jet F. Two jets of fresh air from air-pocket 8--to wit, a first jet .phi..sub.1 flowing through the flap 80 via its open ends 80d and 80e, and a second jet .phi..sub.2 passing directly through orifice 9--are accordingly injected into the gas jet F to produce a silencing effect. When this effect is no longer required, flap 80 pivots about its hinge-pin 81 until its face 80a masks orifice 9 and restores a substantially unbroken surface to the wall 7 of the central body.

FIG. 9 illustrates an alternative possible embodiment of the invention. Depicted in the figure is the central body 5 formed with an orifice 9 downstream of the discharge edge 2a of nozzle 2. Reference numeral 90 designates a deflecting member supported on central body 5 and shaped as a dihedron having an edge 90a.

Responsively to an actuating member 91, deflecting member 90 can occupy a deployed operative position (shown in FIG. 9) in which it projects into the gas jet F through orifice 9, downstream of the discharge edge 2a of nozzle 2. The dihedron edge 90a then extends in a direction having a component transverse to the nozzle axis, the interior of the dihedron then facing the downstream end of the jet engine. In this position the gas jet efflux F is divided by dihedron 90 into two partial jets which mix, on the one hand, with the air jet .phi. passing through orifice 9 and, on the other, with a stream of air from the surrounding atmosphere that penetrates into the dihedron.

This enhances the silencing effect. When the latter is no longer required, deflecting member 90 moves into a retracted inoperative position responsively to actuating member 91, in which position it is retracted into the cental body 5.

As shown in FIg. 10, adjustable obturating means cooperating with the orifice 9 are likewise provided in this particular case. In the illustrated example, such obturating means include a pair of flaps 100, 101 hingedly connected to central body 5 about hinge-pins 102, 103 respectively, each extending in a direction having a component parallel to the nozzle axis. These flaps may occupy either an operative position (shown in FIG. 10) in which the orifice 9 is unmasked, or an inoperative position (not shown) in which said orifice is masked after the deflecting member 90 has retracted into the central body.

FIGS. 11 and 12 show an alternative arrangement of the invention. Shown on these figures is the central body 5 formed with an orifice 9 at least part of which lies downstream of the discharge edge 2a of nozzle 2. An auxiliary fairing, the upstream edge 110a of which has a diameter in excess of the greatest dimension of the downstream portion of the engine cowling 4, is disposed coaxially with the engine.

Actuating means 111 allow of sliding the auxiliary fairing 110 parallel to the nozzle axis whereby to cause it to occupy either an extended position (shown in FIG. 11) in which it is positioned to form an exhaust diffuser around the gas jet F, or an inoperative position (shown in FIG. 12) in which it surrounds the cowling 4.

In its extended position, auxiliary fairing 110 surrounds central body 5 in the region of the orfices 9 (which are then unmasked) and by an ejector effect allows of inducing a stream of outside air A into the gas jet F exhausting through the nozzle 2. This enhances the silencing effect already obtained by injecting streams of air .phi. through the orifices 9. When this silencing effect is no longer needed, the flaps 10 mask the orifices 9 and auxiliary fairing 110 is moved forward once more into its inoperative position shown in FIG. 12.

It goes without saying that changes and substitutions of parts may be made in the non-limitative exemplary embodiments hereinbefore described without departing from the scope of the invention as set forth in the appended claims.

Claims

What we claim is:

1. In and for a jet propulsion engine having a thrust nozzle adapted to exhaust a propulsive gas jet, said nozzle including wall means longitudinally bounding a hollow central body substantially coaxial with said nozzle, a silencer device for reducing the noise produced by said gas jet, said silencer device comprising means for supplying the inside of said hollow central body with air, and at least one orifice formed in said wall means and through which air from the inside of said hollow central body can discharge into the gas jet exhausting from said thrust nozzle, wherein the improvement comprises, hingedly connected to the central body, at least one adjustable obturating flap movable between a first position wherein it unmasks said orifice and a second position wherein it masks the same and restores a substantially unbroken surface to the longitudinal wall of the central body.

2. A silencer device according to claim 1, wherein the flap comprises a hollow body having an open upstream end which always lies inside said central body, and a likewise open downstream end which when said orifice is masked lies inside the central body and when said orifice is unmasked projects into the gas jet.

3. A silencer device according to claim 1, further comprising an adjustable deflecting member in the shape of a dihedron projecting into the gas jet with its edge extending substantially transversely to the nozzle axis when said orifice is unmasked.

4. A silencer device according to claim 1, wherein the flap is hingedly connected to the central body about a hinge line having a component substantially parallel to the nozzle axis.

5. A silencer device according to claim 1, wherein the nozzle comprises a discharge edge situated upstream of the said orifice.

6. A silencer device according to claim 5, further comprising an auxiliary fairing coaxial with the nozzle, said fairing being disposed at least partly downstream of the said discharge edge and having an upstream diameter greater than the largest dimension of the downstream portion of a cowling containing the jet engine.

7. A silencer device according to claim 6, further comprising means for moving said auxiliary fairing in a direction parallel to the nozzle axis, between an extended postion in which the auxiliary fairing functions as an exhaust diffuser around the said gas jet and a retracted position in which it surrounds the said engine cowling.

8. A silencer device according to claim 1, wherein the means for supplying the inside of the hollow central body with air comprise an ejector fed with a pressurized inducing fluid.

9. A silencer device according to claim 1, in and for a jet propulsion engine having an multistage compressor, wherein the means for supplying the inside of the hollow central body with air include at least one passageway originating between two stages of said compressor.

10. A silencer device according to claim 1, in and for a jet propulsion engine of the dual-flow type, namely a heated gas flow and an unheated air flow, wherein the means for supplying the inside of the hollow central body with air comprise means for drawing air from said unheated air flow.